This invention relates to metal flake production technology, more particularly, this invention relates to a knurling tool useful for forming multiple uniform serrated edges on a heat extracting drum such that the drum would have uniform discrete serrations transversely along the peripheral surface, or in other words, parallel to the axis of rotation. In producing metal flake, the leading surfaces of the serrations contact molten material and have formed thereon flake particles.
As used herein the terms flake particles, flakes and flake refer to particles of relatively small size, in the hundreths of an inch range, and the terms include particles frequently referred to as powders because of their relatively small size.
U.S. Pat. No. 4,154,284, commonly assigned, disclosed a method for producing metal flake of small length-to-width ratio directly from a pool of molten metal. Said method involved use of a generally circular serrated-edge, heat-extracting disk-like member touching the surface of a molten pool.
U.S. Pat. No. 4,215,084 disclosed an advancement in the art consisting of a drum-like heat extracting member consisting of a serrated copper-sleeved, water-jacketed drum. Said application disclosed that the flake production rate can be increased by the use of multiple molten streams projected upon a serrated drum-like member. A substantially rectangular flake product is produced. For certain application such as roofing, a flake product with length and width being substantially equal is preferred. The length, width, and thickness of the flake product are influenced and controlled by factors such as the width or diameter and flow rate of the molten metal stream, the viscosity of the molten metal, the speed of rotation of the serrated drum, and the configuration of the serrated drum and serrations, including the length of the angular surfaces and the height of the radial surfaces.
While a serrated drum-like member can markedly increase flake production, manufacture of acceptable serrated drums required painstaking precision to achieve acceptable and reproducible results. Copper drum surfaces are difficult to uniformly serrate while maintaining precise tolerances. On a 22" diameter drum, and a serration of 0.06 inches in width (0.0025" depth) about 1152 uniform transverse serrations are required (22.multidot..pi.+0.06=1152). In addition the angular surface of the serrated drum wears with time and usage thus requires periodic reconditioning. Each serration consists of a radial surface and an angular surface inclined at an angle .theta. to the tangent of curvature of the drum. For optimum flake product dimensions and product uniformity it is necessary that each of the multiple radial and angular surfaces comprising the drum surface be formed substantially uniform in size and orientation, and continuous across the surface of the drum.
It had been the practice to form the serrations in the drum surface by means of repetitive dropping of a weighted (170-190 lbs./force) precisely shaped chisel following incremental movements of the drum. When a full turn of the drum was made and a serrations impacted to the surface, the chisel was incrementally moved sideways and the process repeated. This would continue until the full width of the drum was serrated. Besides being time consuming since thousands of uniform serrations were necessary, the final drum had rows of serrations which were not always in perfect registry with each other. These imperfections would give rise to a coproduced stringly scrap product when flake was being produced.
Later processes used a paddle wheel shaped tool to impress multiple rows of serrations into the drum surface by turning both wheels while in pressed contact. This method also yielded nonuniform serrations often not in registry transversely across the surface of the drum.
The above factors made the metal flake production process expensive in terms of tooling and machining costs. Commercial acceptance of metal flake production using serrated drum technology could be enhanced if efficient precision serrating of the drum surface would be feasible. The present invention provides a knurling tool for forming multiple uniform serrations precise in size and orientation and in registry transversely across the surface of a metal flake forming drum.